A custom resource is used to store most any type of binary data within a resource file. Each custom resource is identified by a unique index or resource ID. Custom resources are extracted from a resource file at run-time using the LoadResData function which takes the index and the format as arguments. For custom resources created using the Resource Editor, the format is the same as the resource type that is entered in the Edit Properties dialog box. The format string must be enclosed in double quotation marks.
When using custom resources, it is necessary to add the code to your application to read and display the data contained in the file. This usually requires the use of Windows API calls. Common data types that might be stored as custom resources are sound (.wav) and video (.avi) files.
Custom resources provide a convenient way to store custom data for an application while keeping the source files hidden from the user.